To determine which compound is white in color, we need to examine the properties of each option. Let's evaluate them one by one:
- Ammonium sulphide: This compound is typically yellow due to the presence of sulphur, reflecting its character as a sulfide compound. Thus, it is not white.
- Lead sulphate: Lead sulphate (\( \text{PbSO}_4 \)) is known to be a white solid and is insoluble in water. This makes it a promising candidate for being the white compound among the given options.
- Lead iodide: Lead iodide (\( \text{PbI}_2 \)) typically appears as a bright yellow solid. Due to its characteristic color, it is not the white compound in question.
- Ammonium arsinomolybdate: Beyond common compounds, this is not as widely recognized and usually involves complex formation with variable colors. Thus, without specific reference indicating otherwise, it can't be assumed to be white.
From the above analysis, we can conclude that among the listed options, lead sulphate is distinctly known for its white coloration.
Therefore, the correct answer is lead sulphate.